There are various kinds of earsets, and an in-ear earphone which receives sound while being inserted an ear canal of an ear flap is generally referred to as an earset.
Meanwhile, as the earset is inserted in the ear canal, an atmospheric pressure difference occurs between the inside (human body pressure) and the outside (atmospheric pressure) of the earset. That is, as an eartip formed in the earset is tightly attached to the inner wall of the ear canal, the atmospheric pressure difference occurs between the inside and the outside of the earset.
However, the atmospheric pressure difference influences a diaphragm, and a phenomenon of shifting the diaphragm toward the outside of the earset occurs.
To prevent the shift of the diaphragm, a back hole exists on the rear side of a dynamic driver unit and a balanced armature driver unit. The back hole performs a function of keeping the pressure inside and outside of the earset equal. Therefore, vibration occurs when the diaphragm is at a right position. In addition, when the back holes are covered by dampers or the like of different mesh densities, a pressure difference occurs when the diaphragm operates, and this may be used for tuning.
However, the back hole has a problem of working as a path for inputting external noises. That is, as shown in FIG. 1, a hole H exists in a case 2 which accommodates a driver unit 1, and the hole H formed in the case 2 and the back hole BH formed in the driver unit 1 work as a path through which external noises flow in. Therefore, the external noises should be perfectly blocked to be used in a place where perfect blocking of the external noises is needed, for example, an airport or the like. However, it is difficult to perfectly block the external noises due to the existence of the hole H formed in the case 2 and the back hole BH formed in the driver unit 1.
Meanwhile, an earset which integrates a speaker and a microphone performs a function of transferring sound to the ear canal and a function of collecting user's voice in one body. In the earset having such a structure, it is general that the speaker is installed toward the ear canal to transfer sound, and the microphone is installed toward the outside of the ear flap to collect user's voice. Therefore, a sound collection hole is formed in the case exposed to the outside of the ear flap so that the microphone may collect sound, and there is a problem in that external noises flow in through the sound collection hole, and the external noises are transferred to the back hole formed on the rear side of the driver unit. Meanwhile, even in the case of the in-ear microphone in which the microphone faces the ear canal, there is a problem in that the sound quality is lowered due to the external noises regardless of the installation position of the in-ear microphone. However, if the back hole formed on the rear side of the driver unit is blocked, a phenomenon of shifting the diaphragm occurs as described above, and it cannot be used in an airplane or a high mountain area.
Therefore, a method of blocking the external noises flowing in through the back hole formed on the rear side of the dynamic driver unit and the balanced armature driver unit, and allowing inflow of air is needed.